revision notes for class 12 cbse chemistry, chemistry in everyday life - topperlearning

CHEMISTRY CHEMISTRY IN EVERYDAY LIFE

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Chemistry in Everyday Life

TOP Concepts Drugs: Drugs are low molecular mass ( 100–500 u) substances which interact with targets in the

body and produce a biological response.

Medicines: Medicines are chemicals which are useful in diagnosis, prevention and treatment of diseases.

Therapeutic effect: Desirable or beneficial effect of a drug such as treatment of symptoms and cure of a disease is known as therapeutic effect.

Enzymes: Proteins which perform the role of biological catalysts in the body are called enzymes.

Functions of enzymes

o The first function of an enzyme is to hold the substrate for a chemical reaction. Active sites of

enzymes hold the substrate molecule in a suitable position so that it can be attacked by the reagent effectively.

o The second function of an enzyme is to provide functional groups which will attack the substrate and carry out the chemical reaction.

The main role of drugs is to either increase or decrease the role of enzyme-catalysed reactions. Inhibition of enzymes is a common role of drug action. An enzyme inhibitor is a drug which inhibits the catalytic activity of enzymes or blocks the binding site of the enzyme and eventually prevents the binding of the substrate with the enzyme. Drugs can inhibit the attachment of the substrate to the active site of enzymes in the following ways.

o Competitive Inhibition: Competitive inhibitors are the drugs which compete with the natural

substrate for their attachment on the active sites of enzymes.



o Non-competitive Inhibition: Some drugs do not bind to the enzyme’s active site but instead bind

to a different site of the enzyme called the allosteric site. This binding of the inhibitor at the

allosteric site changes the shape of the active site in such a way that the substrate cannot

recognise it. If the bond formed between an enzyme and an inhibitor is a strong covalent bond and

cannot be broken easily, then the enzyme is blocked permanently. The body then degrades the

enzyme–inhibitor complex and synthesises the new enzyme.

Receptors as Drug Targets Proteins which are vital for the communication system in the body are called receptors. In the body, the message between two neurons and that between neurons to muscles is communicated through chemical messengers. They are received at the binding sites of receptor proteins. To accommodate a messenger, the shape of the receptor site changes which brings about the transfer of message into the cell. A chemical messenger gives the message to the cell without entering the cell.

Receptors show selectivity for one chemical messenger over the other because their binding sites have different shape, structure and amino acid composition. Drugs which bind to the receptor site and inhibit its natural function are called antagonists. These are useful when the blocking of the message is required. Drugs which mimic the natural messenger by switching on the receptor are called agonists. These are useful when there is a lack of natural chemical messengers.



Therapeutic action of different classes of drugs

o Antacid: Chemical substances which neutralise excess acid in the gastric juices and give relief from acid indigestion, acidity, heart burns and gastric ulcers. Examples: Eno, Gelusil, Digene etc.

o Antihistamines: Chemical substances which diminish or abolish the effects of histamine released in the body and hence prevent allergic reactions. Examples: Brompheniramine (Dimetapp) and terfenadine (Seldane)

o Neurologically Active Drugs: Drugs which have a neurological effect, i.e. affects the message transfer mechanism from nerve to receptor. Tranquillisers: Chemical substances used for the treatment of stress and mild or severe mental

diseases. Examples: Derivatives of barbituric acids such as veronal, amytal, nembutal, luminal and seconal

Analgesics: Chemical substances used to relieve pain without causing any disturbances in the nervous system such as impairment of consciousness, mental confusion, incoordination, paralysis etc.

Classification of Analgesics

Non-narcotic analgesics Narcotic analgesics

They are non-addictive drugs. When administered in medicinal doses, these drugs relieve pain and produce sleep.

Examples: Aspirin, Ibuprofen, Naproxen, Diclofenac Sodium

Examples: Morphine and its derivatives

Antimicrobials: Drugs which tend to destroy/prevent development or inhibit the pathogenic

action of microbes such as bacteria (antibacterial drugs), fungi (antifungal agents), virus (antiviral agents) or other parasites (antiparasitic drugs) selectively.

Types of antimicrobial drugs

o Antibiotics: Chemical substances produced by microorganisms which kill or prevent the growth of other microbes.

Classification of antibiotics on the basis of mode of control of microbial diseases:

Bactericidal Bacteriostatic

Drugs which kill organisms in the body.

Drugs which inhibit the growth of organisms.

Examples: Penicillin, Aminoglycosides, Ofloxacin

Examples: Erythromycin, Tetracycline, Chloramphenicol

Classification of antibiotics on the basis of its spectrum of action:

Broad spectrum antibiotics Narrow spectrum antibiotics

Limited spectrum antibiotics

Antibiotics which kill or inhibit a wide range of Gram-positive and Gram-negative bacteria.

Antibiotics which are effective mainly against Gram-positive or Gram-negative bacteria.

Antibiotics effective against a single organism or disease.

Examples: Ampicillin and Amoxycillin

Examples: Penicillin G



o Antiseptics: Chemical substances which kill or prevent the growth of microorganisms and can be

applied on living tissues such as cuts, wounds etc. Examples: Soframycin, Dettol o Disinfectants: Chemical substances which kill microorganisms but cannot be applied on living

tissues such as cuts, wounds etc. Examples: Chlorine (Cl2), bithionol, iodoform etc. o Antifertility drugs: Chemical substances used to prevent conception or fertilisation. Examples:

Norethindrone, ethinyl estradiol (Novestrol)

Food additives: Food additives are the substances added to food to preserve its flavour or improve its taste and appearance.

Different types of food additives:

S. No.

Name of food additive Examples

1 Artificial sweetening agents: Chemical compounds which give a sweetening effect to food and enhance its flavour.

Aspartame, Sucralose and Alitame

2 Food preservatives: Chemical substances which are added to food material to prevent their spoilage due to microbial growth.

Sugar, Salts, Sodium benzoate

3 Food colours: Substances added to food to increase the acceptability and attractiveness of the food product.

Allura Red AC, Tartrazine

4 Nutritional supplements: Substances added to food to improve the nutritional value.

Vitamins, minerals etc.

5 Fat emulsifiers and stabilising agents: Substances added to food products to give texture and desired consistency.

Egg yolk (where the main emulsifying chemical is lecithin)

6 Antioxidants: Substances added to food to prevent oxidation of food materials. They help in the preservation of food.

Butylated hydroxytoluene (BHT),

butylated hydroxyanisole (BHA)

Soaps o Soap: It is a sodium or potassium salt of long chain fatty acids such as stearic, oleic and palmitic

acids. o Saponification: The process of making soap by hydrolysis of fats or oils with alkalies.



Types of soaps

S. No.

Descriptions

1. Medicated soaps: These soaps are the soft soaps containing substances with medicinal properties. Neem soap and carbolic soaps are common examples of medicated soaps.

2. Shaving soaps: These soaps are potassium sodium stearates and produce lasting lather. They contain glycerol to prevent rapid drying. A gum called rosin is added to these soaps which forms sodium rosinate which lathers well.

3. Transparent soaps: These soaps are prepared by dissolving the soap in ethanol and then evaporating the excess solvent.

4. Floating soaps: These soaps float in water and are prepared by beating tiny air bubbles into the product before it hardens.

5. Soap chips: These are prepared by running a thin sheet of melted soap onto a cool cylinder and scrapping off the soaps in small broken pieces.

6. Soap granules: These are dried miniature soap bubbles.

7. Soap powder and scouring soaps: These substances contain some soap, a scouring agent (abrasive) such as powdered pumice or finely divided sand and builders such as sodium carbonate and trisodium phosphate. Builders help the soaps in its cleaning action.

o Advantages of using soaps: Soap is a good cleansing agent and is 100% biodegradable, i.e.

microorganisms present in sewage water can completely oxidise soap. Therefore, soaps do not

cause any pollution problems.

o Disadvantages of using soaps:

Soaps cannot be used in hard water because hard water contains metal ions such as Ca2+

and Mg

2+ which react with soap to form white precipitate of calcium and magnesium salts.

These precipitates stick to the fibres of the cloth as gummy mass and block the ability of soaps to

remove oil and grease from fabrics. Therefore, it interferes with the cleansing ability of the soap and

makes the cleansing process difficult.

In acidic medium, the acid present in solution precipitate the insoluble free fatty acids which adhere to the fabrics and hence block the ability of soaps to remove oil and grease from the fabrics. Hence, soaps cannot be used in acidic medium.



Detergents

o Detergents are sodium salts of long chain of alkyl benzene sulphonic acids or sodium salts of long

chain of alkyl hydrogen sulphates.

o Classification of detergents

Anionic detergents:

Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons. Alkyl

hydrogen sulphates formed by treating long chain alcohols with concentrated sulphuric acid are

neutralised with alkali to form anionic detergents. Similarly, alkyl benzene sulphonates are obtained by

neutralising alkyl benzene sulphonic acids with alkali.

Example:

Anionic detergents are termed so because a large part of molecule is an anion.

Uses: They are used in household cleaning such as dishwasher liquids, laundry liquid detergents,

laundry powdered detergents etc.

Advantage: They are effective in slightly acidic solutions where soaps do not work efficiently.

Cationic detergents: Cationic detergents are quaternary ammonium salts of amines with

acetates, chlorides or bromides as anions. Cationic parts possess a long hydrocarbon chain and a

positive charge on nitrogen atom.

Example:

Cationic detergents are termed so because a large part of the molecule is a cation.



Use: Because cationic detergents possess germicidal properties, they are used as germicides. Advantage: They have strong germicidal action. Disadvantage: These detergents are expensive.

o Non-ionic detergents: They do not contain any ion in their constitution. They are like esters of

high molecular mass.

Example: The detergent formed by condensation reaction between stearic acid and

polyethyleneglycol.

Use: In making liquid washing detergents. Advantage: They have effective H-bonding groups at one end of the alkyl chain which make them freely water soluble.

Biodegradable detergents: Detergents with straight hydrocarbon chains which are easily decomposed by microorganisms. Example: Sodium lauryl sulphate

Non-biodegradable detergents: Detergents with branched hydrocarbon chains which are not easily decomposed by microorganisms.

revision notes for class 12 cbse chemistry, chemistry in everyday life - topperlearning

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